1. Field of the Invention
The present invention relates to a structure for a movable platen for supporting a portion of an injection mold in an injection molding machine. More particularly, the present invention relates to a movable mold supporting platen that has improved rigidity, as well as improved stability, and that is slidably carried on injection molding machine tie rods.
2. Description of the Related Art
In general, machines for injection molding of plastics articles include a pair of fixed platens that are spaced from each other and that are interconnected by generally four parallel tie rods that have their axes positioned to define a rectangular array. One of the fixed platens remains stationary and is adapted to support one portion of a two or multiple piece injection mold that when assembled or engaged defines a mold cavity to correspond with the outline of a desired molded part. A movable platen is slidably carried on the tie rods between the fixed platens and is adapted to carry a cooperating portion of the mold so that when the movable platen is moved toward the mold-portion-carrying fixed platen the two mold portions come into contact to define therebetween a mold cavity for forming the desired part.
The movable platen is generally a plate-like structure that is of rectangular configuration and includes four bores at the respective corners, through each of which a tie rod extends. A movable platen actuation system is positioned between the non-mold-carrying fixed platen and the movable platen to cause the movable platen to move along the tie rods toward or away from the mold platen, and also to hold the movable platen firmly in position when the mold portions are together, to prevent separation of the molds as molten material is injected into the mold cavity under high pressure.
When the actuation force for moving the movable platen is applied centrally and in a direction parallel to the axes of the tie rods, the movable platen can be a relatively thin plate structure having a thickness sufficient to withstand the axial loads, because the actuation forces do not cause any cocking or tilting of the movable platen relative to the tie rods. However, if non-parallel actuation forces are imposed, such as would be the case in a single-toggle-type clamp actuation mechanism, then a thicker platen can be provided for larger contact area between the tie rod bores of the movable platen and the tie rods to distribute over a larger area the cocking or tilting forces that result from the single toggle clamp actuation arrangement. However, in providing a greater contact area between the movable platen and the tie rods by means of a thicker platen, additional weight is added to the movable platen, which undesirably increases the inertia of the movable platen and slows its movement, thereby increasing the overall molding cycle time.
It is an object of the present invention to provide an improved movable platen structure that overcomes the problems in the previously employed platen structures.
It is a further object of the present invention to provide an improved movable platen that has a greater contact area with the tie rods to minimize wear and that does not have significantly greater inertia.
It is a still further object of the present invention to provide a movable platen that can accept non-axial actuation forces without excessive wear between the tie rod bores and the tie rods.